This invention relates to an improved hydraulic pump, and more particularly to a pump for pumping liquids at pressures up to approximately 3,000 pounds per square inch (psi) by using a combination of mechanical piston reciprocation and hydraulic forces.
In the field relating to pumps for pumping liquids at high pressure and low volumes, it is common to utilize pumps having a relatively small-sized piston, on the order of 1/2-2 inches in diameter, with a very short stroke, less than 1 inch, and to reciprocate the piston at a very high rate of speed, in the range of 1000-3000 revolutions per minute (RPM). Pumps of this general type develop their high pumping flows by the high rate of reciprocation of the piston, rather than through combinations of large piston surface area and driving forces. Pumps of this general class utilize a pumping chamber having spring-loaded inlet and outlet vales, where liquid is drawn into the pumping chamber during the piston suction stroke by the pressure differential across an inlet valve and is pumped out of the pumping chamber during the compression stroke of the piston by the pressure differential across the outlet valve. The pressure differentials required to open the inlet and outlet valves in the pumping chamber are determined by the respective springs selected to hold the inlet and outlet valves in their closed positions. Such pumps can typically pump liquids at the rate of 0.2-3 gallons per minute, and are to be distinguished from other types of pumps which are utilized at considerably higher flow rates.
It is also known to develop so-called diaphragm pumps which utilize a diaphragm membrane in liquid isolation between a pumping chamber and an oil-filled chamber. These pumps typically operate by inducing, through one means or another, a pressure reciprocation in the oil chamber which causes the diaphragm to reciprocate in coincidence and thereby creates in the pumping chamber the necessary liquid pressure fluctuations for drawing liquid into the pumping chamber and forcing liquid out of the pumping chamber. Such diaphragm pumps have been constructed with mechanically reciprocating devices coupled to the diaphragm, or with mechanically reciprocating pistons coupled to the oil chamber for developing the necessary pressure forces for moving the diaphragm. It is not unusual to utilize springs in conjunction with such pumps to cause the diaphragm membrane to seat in a "rest" position, and to utilize the oil pressure developed within the oil chamber to move the diaphragm from the "rest" position.
In all such pumps it is necessary to provide valves to ensure pressure and volume control in the oil chamber and in the pumping chamber under all pumping conditions. For example, the condition where the output liquid line becomes shut off or blocked, some means must be provided for relieving the internal pressures so as to discontinue the pumping reciprocation pressure forces at some predetermined pressure level. Pressure sensors have been used to monitor output pump pressures and to shut off the reciprocating mechanism whenever output pressure reaches a certain predetermined level. Internal valving has been developed to bypass either the fluid in the pumping chamber or the oil in the oil chamber under these conditions, whereby the reciprocation mechanism continues operating but does not continue to develop high pressures. Depending upon particular applications, any of these pressure control mechanisms may be useful in a particular pump. For example, a water pump may utilize a recirculating bypass mechanism coupled into the pumping chamber for recirculating water through the pumping chamber whenever downstream pressure reaches a predetermined level. A paint pump, on the other hand, may utilize an oil chamber recirculating mechanism to control the internal oil chamber pressure levels and thereby limit pumping pressure, to avoid continuously recirculating paint, which recirculation tends to break down the desired paint qualities.
The mechanism for driving a pump of the type described herein is typically an electric motor. The motor may be mechanically coupled to a pump crankshaft, and a reciprocable piston may be connected to the crankshaft, wherein the piston reciprocates within a cylinder filled with oil, and into a chamber also filled with oil. Reciprocation of the piston causes pressure fluctuations within the oil chamber in coincidence with the reciprocation, and these pressure fluctuations may be utilized to drive a diaphragm separating the oil chamber from a pumping chamber. The diaphragm isolates the oil from the pumping chamber but conveys the pressure fluctuations into the pumping chamber, thereby providing a suction and driving means for pumping liquid through the pumping chamber. A primary disadvantage with pumps of this general description is in the relative fragility of the diaphragm membrane separating the two chambers. Since the diaphragm is required to deflect at fairly high rates of speed it will invariably rupture at reasonably frequent intervals, and when a diaphragm rupture occurs the liquid being pumped becomes contaminated with the oil in the pump, and vice versa, usually requiring that the pump be dismantled and thoroughly cleaned. Depending upon the liquids being pumped, a diaphragm rupture may cause contamination to the point where the pump bearings or piston or other pump moving parts are damaged. Introduction of oil from the pump into the liquid being pumped will thoroughly contaminate the liquid which may result in costly or destructive effects in the pumped liquid flow path. For example, if this liquid is paint, oil contamination in the paint may result in the contamination of a significant quantity of paint both downstream and upstream of the pump.
Various devices have been developed to extend the life of a diaphragm in a diaphragm pump, for example, U.S. Pat. No. 4,050,859, issued Sept. 27, 1977, describes an apparatus for an improved diaphragm pump wherein hydraulic shock and mechanical wear to the diaphragm membrane is reduced by providing a circular reed valve member adjacent to the diaphragm. The reed valve member provides a barrier to pressurized hydraulic oil jets from direct impingement upon the diaphragm membrane, and also assists in reducing hydraulic shock effects on the diaphragm membrane.